Wear-resistant, superabrasive compacts are utilized for a variety of mechanical applications. For example, PCD superabrasive compacts are used in drilling tools (e.g., compacts, cutting elements, gage trimmers, etc.), machining equipment, bearing apparatuses, wire-drawing machinery, and in other mechanical systems.
In one particular application, polycrystalline-diamond compacts (“PDCs”) have found particular utility as superabrasive cutting elements in rotary drill bits, such as roller cone drill bits and fixed cutter drill bits. A PDC cutting element or cutter typically includes a superabrasive diamond layer or table. The diamond table is formed and bonded to a substrate using an ultra-high pressure, ultra-high temperature (“HPHT”) process. The substrate is often brazed or otherwise joined to an attachment member such as a stud or a cylindrical backing A stud carrying the PDC may be used as a PDC cutting element when mounted to a rotary drill bit by press-fitting, brazing, or otherwise securing the stud into a receptacle formed in the rotary drill bit. The PDC cutting element may also be brazed directly into a preformed pocket, socket, or other receptacle formed in the rotary drill bit. Generally, a rotary drill bit may include a number of PCD cutting elements affixed to the drill bit body.
Conventional PDCs are normally fabricated by placing a cemented-carbide substrate into a container or cartridge with a volume of diamond particles or crystals positioned on a surface of the cemented-carbide substrate. A number of such cartridges may be typically loaded into an HPHT press. The substrates and volume of diamond particles are then processed under HPHT conditions in the presence of a catalyst material that causes the diamond particles to bond to one another to form a matrix of bonded diamond grains defining a diamond table. The catalyst material is often a solvent catalyst, such as cobalt, nickel, or iron that is used for facilitating intergrowth between the diamond particles.
In one conventional approach, a constituent of the cemented-carbide substrate, such as cobalt from a cobalt-cemented tungsten carbide substrate, liquefies and sweeps from the region adjacent to the volume of diamond particles into interstitial regions between the diamond particles during the HPHT process. The cobalt acts as a catalyst to facilitate intergrowth between the diamond particles, which results in bonds between adjacent diamond particles. Often, a solvent catalyst may be mixed with the diamond particles prior to subjecting the diamond grains and substrate to the HPHT process.
The solvent catalyst dissolves carbon from the diamond particles or portions of the diamond particles that graphitize due to the high temperature being used in the HPHT process. The solubility of the stable diamond phase in the solvent catalyst is lower than that of the metastable graphite under HPHT conditions. As a result of this solubility difference, the undersaturated graphite tends to dissolve into solvent catalyst and the supersaturated diamond tends to deposit onto existing diamond particles to form diamond-to-diamond bonds. Accordingly, diamond particles become mutually bonded to form a matrix of PCD with interstitial regions between the bonded diamond grains being occupied by the solvent catalyst.
The presence of the solvent catalyst in the diamond table is believed to reduce the thermal stability of the diamond table at elevated temperatures. For example, the difference in thermal expansion coefficient between the diamond grains and the solvent catalyst is believed to lead to chipping or cracking in the PDC during drilling or cutting operations, which consequently can degrade the mechanical properties of the PDC or cause failure. Additionally, some of the diamond grains can undergo a chemical breakdown or back-conversion to graphite via interaction with the solvent catalyst. At extremely high temperatures, portions of diamond grains may transform to carbon monoxide, carbon dioxide, graphite, or combinations thereof, thus, degrading the mechanical properties of the PDC.
One conventional approach for improving the thermal stability of PDCs is to at least partially remove the solvent catalyst from the PDC by acid leaching. However, removing the solvent catalyst from the PDC can be relatively time consuming for high-volume manufacturing. Therefore, manufacturers and users of superabrasive materials continue to seek improved thermally stable superabrasive materials and processing techniques.